# How do i read a frequency graph?

How do i read a frequency graph??

If i have. a time required of 5-9 and a a frequency of 5. how do i find the average? do i do 9-4*6 or 9*5+5*9/5 ?? thanks.

Mark44
Mentor

If i have. a time required of 5-9 and a a frequency of 5. how do i find the average? do i do 9-4*6 or 9*5+5*9/5 ?? thanks.

I don't think you have given a clear explanation of what you are given, but I'll do my best to explain what I think you are asking. Also, I don't think that either of the values you gave is correct. 9 - 4*6 = 9 - 24 = -15, which doesn't make any sense. If you meant (9 - 4)*6, that's 5*6 = 30, and I don't see that this number has anything to do with anything. For the other expression, 9*5+5*9/5 = 45 + 9 = 54, but that doesn't have anything to do with anything, either.

I believe that the time required, 5 - 9, means a time interval of 5 to 9 time units of some kind, and the frequency of 5 means that 5 times were between 5 and 9 (sec? min? hours?).

The average time would be (5 + 9)/2 = 7

Sorry i meant.
|Time required to complete test| Frequency | Midpoint |
| 5-9 | 6 | 7 |
| 10−14 | 12 | 12 |
| 15−19 | 25 | 17 |
| 20−24 | 34 | 22 |
| 25−29 | 16 | 27 |
| 30−34 | 7 | 32 |

What would be the mean of this? sorry.

Would i just do total of (frequency * midpoint)/amount scores?

Mark44
Mentor

Something like that. For each category, multiply the frequency by the midpoint of the category. Add all these products and divide by the total frequencies. IOW,
(f1 * m1 + f2 * m2 + ... + fn * mn)/(f1 + f2 + ... + fn)

Thank you. Do you know how i'd go around getting the stadard deviation? Is it root(x-mean)^2/n?